Typically, light-emitting devices, which do not need an external light source and are self-luminous, are advantageous because of high light-emitting efficiency, superior luminance and viewing angles and fast response rates, but are disadvantageous because moisture or oxygen in the atmosphere infiltrates the light-emitting device and thus the electrode may be oxidized or the device itself may deteriorate, undesirably shortening the device lifetime. Hence, thorough research into the fabrication of light-emitting devices stable to moisture or oxygen is ongoing.
Also, when organic electroluminescence (EL) devices are driven for a predetermined period of time, emission properties including luminance, light-emitting efficiency and emission uniformity may more remarkably deteriorate compared to when they are initially used. The reason why the emission properties deteriorate may include for example electrode oxidation due to oxygen infiltrating the organic EL device, oxidation and decomposition of an organic material caused by heating during operation, and denaturalization of an organic material. Also, the reason why the emission properties deteriorate may further include mechanical degradation of the structure thereof. For instance, interfacial exfoliation of the structure may be caused by oxygen or moisture, and also, may result from stress induced at the interface of the structure because of respective constituents having different coefficients of thermal expansion depending on heat generated in the course of the device being driven and on heat conditions.
In order to prevent such problems, various attempts have been made to seal organic EL devices in order to inhibit contact with moisture or oxygen. For example, there is disclosed a method of preventing moisture from reaching an organic EL device by placing a sealing cap 2 having an absorbent 6 adhered to the inner wall thereof on a picture element area of an organic EL device comprising a substrate 1 and a transparent electrode 3, and an organic functional layer 4 and a metal cathode 5 which are formed on the substrate 1, filling the space therebetween with nitrogen gas 9, and then attaching the sealing cap 2 to the substrate 1 using an adhesive 7, as shown in FIG. 1.
As such, a variety of materials to use for the absorbent 6 have been studied. Particularly, thorough research into alkali earth metal oxides such as barium oxide (BaO) or calcium oxide (CaO) continues because they are able to specifically capture water molecules using a chemical reaction and do not discharge water molecules at high temperature, unlike water absorbents which physically adsorb water, such as silica gel or zeolite.
However, the absorbent 6 used is composed of inorganic compound particles and requires that a concave member be adapted to adhere to the device, undesirably making the resulting device thick.
Furthermore, because alkali earth metal oxides are opaque, they may be applied to so-called bottom emission type display devices for emitting light from the substrate 1. Whereas, in the case where alkali earth metal oxides are applied to so-called top emission type display devices for emitting light from the sealing cap 2 opposite the substrate 1, light emission may be blocked by the absorbent 6, and thus the absorbent 6 should be disposed so that it does not enter an image picture area and the mounting position should be provided.
When the absorbent is applied to top emission type display devices, for example, the use of a water absorbent comprising a polymer such as polyvinylalcohol or nylon which is transparent and is able to absorb water may be easy to conceive of. However, these polymers physically absorb water and do not have sufficient water absorption properties.
Japanese Unexamined Patent Publication No. 2001-357973 discloses the use of a particulate water absorbent disposed so as not to adversely affect light transparency in a top emission type structure, and also Japanese Unexamined Patent Publication No. 2002-56970 discloses the use of a plastic substrate in which there is dispersed a water absorbent that has particles the size of which is smaller than the light emission wavelength of organic EL devices. However, it is difficult to dispose the inorganic particles and also to uniformly disperse them as primary particles, unavoidably lowering light transparency due to the scattering of light.
Accordingly, the present invention is intended to provide an absorbent and a passivation layer for an optical element, which may prevent moisture from infiltrating an optical element.
Also, the present invention is intended to provide an absorbent and a passivation layer for an optical element, which may be applied to dual emission type display devices because of high light transmittance without blocking light.
Also, the present invention is intended to provide an absorbent and a passivation layer for an optical element, which may be applied to flexible displays.
Also, the present invention is intended to provide a passivation layer for an optical element, which may prevent an optical element from deteriorating so as to maintain emission properties during extended use.
A first preferred embodiment of the present invention provides an absorbent comprising a compound represented by Formula 1 below or a compound represented by Formula 2 below:
wherein R1, R2 and R3, which are the same as or different from each other, each are independently selected from among an alkyl group, a cycloalkyl group and an aryl group, M is selected from among trivalent metals, and X is an integer of 1˜1000.
In this embodiment, the absorbent may have a light transmittance of 50% or more at 550 nm.
A second preferred embodiment of the present invention provides a passivation layer for an optical element, comprising a compound represented by Formula 1 below or a compound represented by Formula 2 below:
wherein R1, R2 and R3, which are the same as or different from each other, each are independently selected from among an alkyl group, a cycloalkyl group and an aryl group, M is selected from among trivalent metals, and X is an integer of 1˜1000.
In this embodiment, the passivation layer for an optical element may further comprise a thermoplastic resin.
In this embodiment, the thermoplastic resin may have a moisture content of 100 ppm or less.
In this embodiment, the thermoplastic resin may have a softening point of 50˜200° C.
In this embodiment, the passivation layer for an optical element may have a light transmittance of 50% or more at 550 nm.
In this embodiment, the optical element may be selected from among an organic light-emitting device (OLED), a semiconductor, a liquid crystal display (LCD), a plasma display panel (PDP), and a solar cell.
A third preferred embodiment of the present invention provides an optical element, comprising the absorbent according to the first embodiment.
A fourth preferred embodiment of the present invention provides an optical element, comprising the passivation layer according to the second embodiment.